High-frequency tube



Patented June 9, 1953 HIGH-FREQUENCY Donald E. Harris and Ralph L.McQreary, Cedar Rapids, Iowa, assignors to Collins Radio Company, CedarIowa Rapids, Iowa, at corporationof Application January 8, 1951, SerialNo. 204,882

v2 Claims. (01. 31sec) This invention relates in general to electronicdevices and in particular to ultra-high frequency tubes.

In the field of electronics, engineers have continuously pushed tohigherfrequencies for transmission of radiant energy. Reasons for thisare that, due to the large number of transmitting stations morefrequencies are needed for new transmitters and secondly, transmissionat the higher frequencies is oftentimes accomplished with a minimum ofinterference caused by variations in the Heavyside layer and similardisturbing factors. One highfrequency' electronic device is theklystron, which has a'bunching cavity through which an electron beam ispassed and which bunches the electrons proportional to the frequency ofthe cavity. The electrons pass through a drift space where furtherpunching occurs and into an anode cavity which is resonant at thebunched frequency and thus driven b the electron stream. The output ofthe anode cavity is removed by a coupling loop. The disadvantages of theklystron are that the electron gun is never turned off and thus thecathode gives a constant output. This'results in .a relatively lowefficiency and a theoretical maximum efficiency of 57%.

The resnatron is another high frequency electronic device which has aresonant circuit comprising the gridand the cathode. An anode is placedso as to intercept electrons passing from the cathode. The resnatron isconstructed as a radial structure wherein a center cathode is surroundedby a concentric grid structure and an outer concentric plate. The gridcontrols the electron flow from the cathode and can cut it off so thatthe tube can be operated in class C fashion. This results in greatlyincreased efficiency. Due to the concentric arrangement of the resnatrontube, the size of the cathode is of necessity relatively small and theemission current is limited thereby.

It is an object of this invention, therefore, to provide an electronicdevice which may be operated in class C fashion by obtaining a highemission current from the cathode.

Yet another object of this invention is to provide an axially alignedelectronic device which has a control grid forming part of the resonantcathode that will turn oif the cathode during a part of the cycle.

Yet another object of this invention is to provide an improved highlyefficient electronic dev1ce.

A feature of this invention is found in the provision for an anode and acathode spaced in nated generally as ID, in which is mounted an anode Hwhich is generally cylindrically shaped. The upper wall 12 oftheanode II is formed with a cone shaped portion I3 at its center and the oppositewall I4 is formed with a central opening It. The anode II is supportedfrom the envelope Ill by mechanical supports ll.

A cathode, designated generally as I3, is generally cylindrically shapedand is formed in two sections including an upper section l9 and a lowersection 2 I. The lower section 2| has a bottom 2.2 and upwardlyextending side walls '23. The bottom .22 is formed with a centercupshaped extrusion24. The upper section I9 is smaller in'radius thanthe lower section 2i and has a top 26 and downwardly extending walls 21.The walls 27 fit concentrically within the walls 23. Resistive materialas, for example, a thin layer of ceramic 23, is placed between the outeredge of wall 21 and the inner edge of ,wall 23. The material 28 thusinsulates the member [9 from the member 21 for a direct currentpotential. For alternating frequencies, however, the material 28 offersvery little impedance and thus it provides means for maintaining themember :9 at a direct current potential differentfrom that of the member2| while they are at the same high frequency potential. The cathode i8is supported from the envelope it by the mechanical supports 28.

The cup-shaped portion 24 is coated on its inner surface with anemitting material 26 and a heater. '25 heats the cup-shaped portion 24to cause electron emission from the inner surface thereof.

An input loop 29 passes through the wall 22 and has its end connected toit. In the anode cavity ll an output loop 3| passes through the wall 12and connects to the inner wall.

A lead 32 is connected to the anode H and passes out through the wall ofthe envelope lil. A second lead 33 connects to the wall 2! of thecathode and passes out through the wall of envelope It. A lead 34connects to the wall 27 of the cathode and passes through the side Wallof the envelope. An accelerating direct current voltage Eb is connectedbetween the leads 32 and 33 with the positive side connected to the lead32. A direct current biasing voltage E is connected between the leads 34and 33 with the negative side of the voltage connected to the lead 34.

In operation, the envelope i0 is evacuated and the heater 25 isconnected to a heating voltage so as to raise the temperature of thecathode 24 high enough to cause electron emission from the material 26.The shape of the member 24 causes focusing of the electrons emitted fromthe inner surface and, providing that the correct bias is placed on themember 58, the electrons will pass through the cathode cavity and outthe opening 36 formed in the wall 26. The electron stream will interactwith the cathode cavity 18, and will be modulated by the resonantfrequency of the cavity so that bunching will occur in the drift spacebetween the opening 36 and opening [6. It may prove desirable to placean external magnetic field so as to pass flux between the cathode andanode and thus aid in focusing the electron beam.

The electrons enter the anode cavity through the opening 16 and impingeon the target 13. As they traverse the anode the bunched electronsexcite and drive the anode cavity so that energy may be removed by thepick-off loop 3!. The operation thus far described is similar to that ofa klystron. Because of the insulation between the members l9 and ill ofthe cathode, however, the electron beam may be turned off during aportion of the cycle so that the tube may be operated in class Cfashion. This means that the electron beam is periodically interruptedso that greater efficiency may be obtained.

This is illustrated in Figure 2. The input exciting voltage supplied bythe lead 28 is near the resonant frequency of the cavity Ill and thedirect current voltage EC placed on the lead as prevents the electronbeam from passing out of the opening 36 except on-the positive peaks ofthe exciting voltage. Thus, as shown in Figure 2, the electron beamemerges from the opening 35 only at times when it is above the biasingvoltage, EC. This results in the tube operating in class C fashion, thusgreatly increasing the efficiency. Thus the electron stream will beturned on and off so that pulses will be released from the cathodecavity. These pulses will be received through the opening IS in theanode which is tuned to substantially the same resonant frequency as thecathode and thus the pulses will excite oscillation of the anode cavityat a high energy level. The output loop 31 will remove this energy.Since the tube is operated in class C fashion the emission of thecathode is not constant and thus a. high level of emission is notconstantly required.

The electrons which flow through the drift space between the cathode andanode tend to bunch due to the variable slope of the bias on the memberl9. This increases the concentration of energy.

Although this invention has been described with respect to a preferredembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention as deflned by the appended claims.

We claim:

1. A high frequency electronic device comprising, an evacuated envelope,an anode structure whollywithin and supported by said envelope, acathode structure supported within said envelope in axial alignment withsaid anode, said anode comprising a relatively short hollow cylindricalmember, one end wall of said hollow cylindrical member formed with acentral opening,'

said cathode comprising, a pair of discs with short peripheral flanges,the flange of one of said discs mounted telescopicall within the flangeof the other disc, said discs being spaced remote from each other, saidflanges telescopically overlapping each other, and the first of saiddiscs formed with a central opening in axial alignment with said anode.

2. A high frequency electronic device comprising, an evacuated envelope,a hollow cylindrical anode mounted within said envelope, a pair of endwalls forming a part of said anode, the first end wall formed with acentral opening, the other end wall formed with a central cone-shapedportion, a cathode mounted within said envelope, said cathode comprisingfirst and second discs with short peripheral flanges, the flange of oneof said discs mounted telescopically within the flange of the otherdisc, said discs being spaced remote from each other, the first of saiddiscs formed with a central opening, the other disc depressed into agenerally focusing cathode surface, a heater mounted adjacent the seconddisc behind the cathode surface, and the anode and cathode mounted inaxial alignment so that a stream of electrons emerging from the openingin said first disc will pass into the anode through the opening formedin the first end wall.

DONALD B. HARRIS. RALPH L. MCCREARY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,425,748 Llewellyn Aug. 19, 1947 2,484,643 Peterson Oct. 11,1949

